Structure-Based Optimization of Small-Molecule Inhibitors for the β‑Catenin/B-Cell Lymphoma 9 Protein–Protein Interaction

Abstract

Structure-based optimization was conducted to improve the potency, selectivity, and cell-based activities of β-catenin/B-cell lymphoma 9 (BCL9) inhibitors based on the 4′-fluoro-<i>N</i>-phenyl-[1,1′-biphenyl]-3-carboxamide scaffold, which was designed to mimic the side chains of the hydrophobic α-helical hot spots at positions <i>i</i>, <i>i</i> + 3, and <i>i</i> + 7. Compound <b>29</b> was found to disrupt the β-catenin/BCL9 protein–protein interaction (PPI) with a <i>K</i>_i of 0.47 μM and >1900-fold selectivity for β-catenin/BCL9 over β-catenin/E-cadherin PPIs. The proposed binding mode of new inhibitors was consistent with the results of site-directed mutagenesis and structure–activity relationship studies. Cell-based studies indicated that <b>29</b> disrupted the β-catenin/BCL9 interaction without affecting the β-catenin/E-cadherin interaction, selectively suppressed transactivation of Wnt/β-catenin signaling, downregulated expression of Wnt target genes, and inhibited viability of Wnt/β-catenin-dependent cancer cells in dose-dependent manners. A comparison of the biochemical and cell-based assay results offered the directions for future inhibitor optimization